Antimony oxide products have been used for many years in plastics and textiles to increase the flame resistance properties of the treated material. Antimony oxide pigments have been added with only limited success because the well-known antimony oxide pigment particles are too large e.g. (0.5-3 microns) to obtain maximum effect. Antimony pentoxide has been hydrolyzed in situ onto the material to be treated but these treatments have resulted in only limited success.
A method for preparing an antimony trioxide sol is described in U.S. Pat. No. 3,676,362 in which an antimony trichloride is dissolved in an organic solution, treated with NH.sub.4 OH to produce NH.sub.4 Cl and antimony trioxide. The NH.sub.4 Cl is removed and the antimony trioxide is present as a sol in the solution. The prior art also teaches that an antimony pentoxide sol is more effective than trivalent antimony oxide when added as a flame retardant agent.
One prior art method of preparing the antimony pentoxide sol is described in U.S. Pat. No. 3,860,523. In this procedure a solution of potassium antimonate (containing 2% by weight of antimony calculated as Sb.sub.2 O.sub.5) is passed through a hydrogen form cation exchange resin whereby the potassium ions are exchanged for hydrogen ions to yield a pentavalent antimony oxide sol. In practice, however, it has been found that the low concentration of antimony pentoxide obtained by this process requires an additional evaporation step to obtain a sufficiently high concentration of antimony to be of real commercial value. This separate evaporation step adds to the cost of the operation which is undesirable.
Other prior art methods are described which show that antimony pentoxide may be formed from antimony trioxide by treating the antimony trioxide with HCl to form antimony trichloride which in turn is oxidized to antimony pentoxide by reacting the antimony trichloride with hydrogen peroxide and subsequently hydrolyzing the antimony values to form hydrates of antimony pentoxide. The prior art attempts to prepare sols of these hydrates have failed, however, in producing stable sols having concentrations above 10% solids. Again the evaporation costs to produce higher concentrations are undesirable.
The instant invention covers the preparation of an antimony pentoxide sol composition which is stable upon standing and has a concentration of antimony pentoxide from 25% to 35%. This type of sol is particularly useful as a commercial product in plastics and textiles for improving the flame retardant properties since the sol does not have to be concentrated before use.